In one form of a method for starting up a gasifier, that is to say heating it up, for conversion of carbonaceous fuel in a fluidised bed, for example in the case of a HTW-gasifier (HTW =High Temperature Winkler), the procedure is such that the gasifier is first filled with an inert gas such as nitrogen, and put under pressure, and checked in respect of gas-tightness. The gas-tightness check is ccarried out using inert gs so that oxygen-bearing gas components which, in spite of the preceding flushing operation using the inert gas, still occur in the gasifier or in the lining thereof, and which could result in undesirable reactions, are removed or are diluted down to a harmless level of concentration.
Following the checking operation, the gasifier is heated up in pressure-less condition to a temperature which at least corresponds to the subsequent gasification temperature, for example between 800 and 1000.degree. C. The heating operation is carried out using as burners which are referred to as heating-up burners. The fact that the heating-up temperature has been reached, in other wordsd the gasifier is ready for regular operation, is detected by measurements taken at the top of the gasifier.
After the conclusion of the starting or heating-up phase, the heating-up burners are disassembled in the hot condition while at the same time all the feed of inert gas is shut down. At the locations at which the heating-up burners were removed, the openings are then closed off with cover members. Because of the possibility of a back flow of hot gases, the operation of removing the burners from the heated-up gasifier can only be carried out with substantial safety precautions being taken.
After the openings of the heat-up gasifier have been closed off with the cover members, the gasifier is flushed again with inert gas in order to drive out any oxygen-bearing gases which may have been able to pass into the gasifier in the operation of removing the burners. That repeated introduction of inert gas is also effected while the gasifier is in a non-pressurised condition, but it is disadvanatageous as in that operation the gasifier inevitably cools down. However the temperataure at which the gasifier still remains, namely about 500 to 600.degree. C., is sufficient to ignite ignition fuel, for example lignite or brown coal coke, which is introduced into the gasifier, and to start off the gasification process, with a progressive feed or oxygen-bearing gasification agent. In that procedure, the amount of oxygen supplied with the gasification agent is only such that sub-stoichiometric reaction of the igniting fuel can occur in order at any event to avoid the presence of unreacted oxygen in the gasifier. The fuel feed is increased and, as that feed increases, the temperature rises until finally the gasifier can be switched over to the regular mode of operation thereof, with a continuous feed of fresh fuel and oxygen-bearing gasification agent.
It will be seen from the foregoing that the above-discussed method of heating up or starting a gasifier is a difficult operation and can only be carried out when using expensive and extensive safety precautions. In addition a considerable amount of the energy introduced is lost again due to the necessary inerting operation faer the initial heating-up process.